Sen. Lindsey Graham (R-S.C.) threw down a gauntlet and gave House Democrats a stern ultimatum on closed door testimony he claims will help exonerate the president against their accusations.

“If House D’s refuse to release full transcript of Volker testimony as requested by Congressman Jordan, it will be an abuse of power,” Graham tweeted.

“If this continues, I will call Volker before the Senate Judiciary Committee to testify publicly to ensure the full story is told,” he added in a second tweet.

Graham was referring to testimony from Kurt Volker, the former ambassador to Ukraine, about claims by a whistleblower that the president was improperly demanding political favors in return for military aid.

The accusation is the central claim in the House Democrats’ push for a formal impeachment inquiry.